Calkinsite-(Ce)

calkinsite-(Ce)

burbankite

lanthanite

ancylite

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Formula: Ce2(CO3)3.4H2O
Hydrated normal carbonate, cerium-bearing mineral
Specific gravity: 3.28
Hardness: 2½
Colour: Pale yellow
Solubility: Effervesces strongly in cold dilute (1:5) hydrochloric acid (Mindat)
Weakly RADIOACTIVE
Environments

Hydrothermal environments

Calkinsite occurs in carbonate veins as a weathering product closely associated with burbankite (Webmin).

Localities

At the Central Khanneshin deposit, Khanneshin complex, Reg District, Helmand, Afghanistan, calkinsite-(Ce) is associated with dolomite, khanneshite, carbocernaite, mckelveyite-(Y), baryte and chlorite (HOM).

At the Vuoriyarvi alkaline-ultrabasic massif, Northern Karelia, Murmansk Oblast, Russia, calkinsite-(Ce) is associated with baryte, strontianite and pyrite (HOM).

At the type locality, the Vermiculite prospect No. 6, Big Sandy Creek, Bearpaw Mountains, Hill county, Montana, USA, the mineral deposits occur in shonkinite, mafic monzonite and syenite. Sanidine, biotite, aegirine, calcite, pyrite and pyrrhotite are the major minerals in these deposits. At this locality, shonkinite is irregularly fractured and is host to interconnecting veins, up to 8 inches thick. Calcite is the dominant mineral, and the other minerals are burbankite, calkinsite-(Ce), sanidine, biotite, aegirine, pyrrhotite, pyrite, chalcopyrite, galena, tetrahedrite, ilmenite, baryte, ancylite and lanthanite.
In unweathered specimens the veins are essentially burbankite intricately veined by very fine grained ancylite and subordinate amounts of calcite and biotite. Burbankite is also disseminated in calcite as anhedral crystals commonly less than 0.02 mm in size. As a result of weathering, the burbankite-ancylite intergrowth is altered to a porous, flaky, powdery material containing plates of calkinsite-(Ce), lanthanite, fine-grained baryte, goethite, and some other unidentified minerals. Calkinsite-(Ce) is most abundant in the partly altered area adjacent to unweathered burbankite, and lanthanite and baryte are most abundant in completely altered material. Both calkinsite-(Ce) and baryte are present also in rare vugs that show no evidence of weathering. The plates of calkinsite-(Ce) are less than 1 mm in size.
In the sequence of mineral development, burbankite is younger than most of the calcite; ancylite was formed locally by a reaction on burbankite by a hydrothermal solution. In this reaction burbankite contributed to form a hydrous complex carbonate richer in rare earths. Both of these complex carbonates were decomposed to form calkinsite-(Ce) and lanthanite. This final decomposition most probably was caused by weathering, and further resulted in deposition of baryte, goethite and an unidentified sulphate (AM 38.1169-1183).

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